Cherenkov Telescope Array Mirror Alignment Report

Abstract

The Cherenkov Telescope Array (CTA) is a groundbased observatory for gamma rays with very high energy characteristics within the range of 10 GeV to 100 TeV. It is currently still under development. As the title of the project suggests, it takes advantage of the Cherenkov radiation that is produced by the gamma ray’s interaction with the earth’s upper atmosphere, similar to the guiding physical principles of VERITAS. The primary differences are that CTA will feature more telescopes and possess a larger energy range. Cherenkov radiation will be collected by an array of dozens of optical telescopes of various sizes. These optical telescopes will be composed of hexagonal mirrors that must be aligned relative to each other so as to represent the shape of the telescope as a whole properly. It was in this area of research that my efforts were focused. The most recent proposed system with which to align the mirrors consists primarily of a laser and a webcam. Sixty to three hundred snapshots are taken of the laser and the position of the laser’s centroid in each frame is measured and analyzed by a custom-written computer program executed via ROOT. One to ten microns was the ideal resolution that was required of the system to meet the needs of this project. Since the position of the laser’s centroid was given by pixel number, it was necessary to determine the ratio of pixels to millimeters via another ROOT program described in more detail on the following pages. It was also necessary to ensure by using an OPENCV analysis program that the pixels were not saturated. As will be shown, the consequences of saturation are bothersome edge effects that produce erroneous results.

Related Papers

• → The next generation Cherenkov Telescope Array observatory: CTA(2014)14 cited
• → Normalized and asynchronous mirror alignment for Cherenkov telescopes(2016)8 cited
• → Comparison of Different Trigger and Readout Approaches for Cameras in the Cherenkov Telescope Array Project(2013)2 cited
• → A Prototype Data Format for the Cherenkov Telescope Array: Regions Of Interest (ROI)(2015)